Expansible chamber hydraulic cylinders having moveable piston-and-rod assemblies therein are widely used on industrial, earthmoving, and material handling machines and vehicles. It may be advantageous for such a machine or vehicle to include an automatic control system for automatically controlling the extension or retraction of a piston-and-rod assembly within a hydraulic cylinder so that partially or totally automatic work operations may be performed. In one type of automatic control system, a position sensor may be attached to a hydraulic cylinder to determine the position of the piston-and-rod assembly within the cylinder. One challenge with using such a position sensor is creating a robust, accurate, and affordable mount and mounting method for coupling the position sensor with the hydraulic cylinder.
International Patent Application No. PCT/FI93/00285, International Publication No. WO 95/01510, discloses a hydraulic cylinder with means for determining the position of a piston rod relative to a cylinder sleeve. The means consist of (i) optically readable marks provided on the surface of the piston rod and (ii) a reading device for reading the marks. The reading device is supported on the cylinder sleeve and is positioned in a mechanically protected structure, which constitutes part of a sealing/bearing end piece of the cylinder.
U.S. Pat. No. 5,455,509, issued to Semura et al., discloses a device for mounting a position-detecting sensor to a hydraulic cylinder. Semura discloses a piston rod with a magnetic scale formed on the outer surface thereof and a magnetic sensor mounted on a cylinder head proximate the magnetic scale for detecting the magnetic scale and determining the position of the piston rod. The sensor is mounted on a block, and the block is mounted on the head of the cylinder by a plurality of bolts.
Prior sensor mounting devices and methods may be improved by providing better arrangements and methods for mounting a sensor in proper alignment with detectable features formed on the rod of a cylinder assembly. For example, if (i) detectable features are disposed along the length of a rod member, (ii) the rod member is assembled in a predetermined rotational orientation within a cylinder body, and (iii) a sensor is mounted in a predetermined orientation on a head or gland member, the gland member must be assembled in a predetermined rotational orientation relative the cylinder body in order for the sensor to be properly rotationally aligned with the detectable features of the rod. However, when a threaded gland member is threaded into a threaded end of a cylinder body, the threaded gland member is typically threaded very tightly into the end of the cylinder body so that a frictional engagement is created between a flange portion of the gland member and the end of the cylinder body. The frictional engagement creates a frictional force sufficient to hold the gland member in position relative the cylinder body during operation of the cylinder assembly. The final rotational position of the gland member relative the cylinder body (and relative the detectable features of the rod) is often difficult to predict or predetermine since (i) the final position of the gland member relative the cylinder body will ultimately depend upon the arrangement of the threads of the gland member relative the flange portion thereof and relative the threads of the cylinder body, and (ii) it is often difficult and/or expensive to manufacture threaded glands and threaded cylinder bodies so that the threads thereof are consistently arranged and engaged exactly as desired.
Further, prior sensor mounting devices and methods may be improved by providing better arrangements and methods for maintaining the alignment of a sensor with detectable features on a cylinder assembly during operation of the cylinder assembly.
The present invention is directed at overcoming one or more problems or disadvantages associated with prior sensor-mounting devices and methods.